The present invention relates generally to methods and systems for producing fiber reinforced composite components using a pultrusion process. More specifically, the present invention relates to composite components that utilize a polyurethane resin matrix.
Fiber-reinforced composite structural components that are formed in a pultrusion process typically include a fibrous reinforcing material (e.g., glass, polymeric, or carbon fibers) embedded in a resin matrix (e.g., a polymer such as an unsaturated polyester or epoxy vinyl ester). The fibrous reinforcing material typically includes both yarns or tows (each of which include a large number of fibers or filaments) and one or more mats or webs of fibers.
To produce composite structural components such as lineals for use in windows and doors, the tows are coated by pulling them through an atmospheric pressure bath (typically an open vat or tub) of liquid resin precursor material. Once coated, the tows are pulled through a curing die to polymerize and set the resin. One difficulty with using atmospheric pressure baths to coat the tows is that the individual fibers or filaments within the tows may not be adequately coated with resin. For example, the outer surface of the tows may be coated with resin, while the filaments or fibers on the inside of the tows may be only partially coated.
Because the strength of the composite structural component is largely dependent upon the interaction between the resin matrix and the fibrous reinforcement, it is desirable to completely coat as many of the individual filaments or fibers as possible. Uncoated filaments are not structurally supported, and are unable to take any significant compressive load. In addition, void areas intermingled with the filaments become sites where cracks will initiate under load, thereby reducing both the stiffness and the strength of the composite component. Thus, it would be advantageous to reduce the number of partially coated filaments, voids, or the like that are present in the finished component.
Another difficulty associated with atmospheric pressure baths is that they generally contain a relatively large volume of uncured resin precursor chemicals, and a large surface area of these chemicals is exposed to the atmosphere. Vaporization of such chemicals into the surrounding atmosphere may be undesirable, and mitigation systems designed to reduce the vapor emissions may be relatively costly and may impede many of the tasks required to maintain product quality and productivity.
Conventional resins used in the production of pultruded composite components (e.g., polyesters, vinyl esters, phonolics, etc.) have an ultimate strength of between approximately 8,000 and 15,000 psi, and an elastic modulus between approximately 350,000 and 500,000 psi. This elastic modulus is well matched to that of the reinforcing fibers. When a compression or bending load is applied to such a composite component, the load is shared among the reinforcing fibers in a manner that results in relatively balanced loading and relatively high ultimate strength. However, the elongation-to-failure of these conventional resin systems is typically between approximately 1.5% and 3%, and is exceeded before that of the fibers, which may have an elongation-to-failure of 4% to 6%. The resin will fracture when its elongation-to-failure is exceeded, leaving the fibers unsupported. This allows the load to concentrate in a small percentage of the available fibers, exceeding their ultimate strength and resulting in the failure of the component at loads that are below the theoretical maximum of the complete fiber reinforcement package.
Conventional resins used in the production of pultruded composite components also have relatively little strength in the direction transverse to the longitudinal (i.e., pulling) direction. As a result, pultruded composite components may utilize reinforcing fibers oriented in the transverse orientation to provide the necessary transverse strength for the component. For example, the reinforcing material may include both fiber tows that extend through the pultruded component in the longitudinal direction and fiber mats that provide multidirectional strength for the component. However, the inclusion of transverse fibers or fiber mats undesirably adds weight and cost to the component and also adds processing difficulties to the production of the component.
Accordingly, there is a need to provide an improved resin system to provide enhanced structural strength for pultruded composite components as compared to that provided by conventional resin systems. There is also a need for a composite component that does not utilize transverse reinforcing fibers but that has sufficient transverse strength to provide resistance to bending and to allow the component to be secured with screws, nails, or the like. There is further a need to provide an improved system and method for coating reinforcing materials with a polymeric material in a pultrusion process.